Electronic control circuit with time delay of main and feedback signals

ABSTRACT

An electronic control circuit particularly adaptable for use in a heating and/or cooling control system wherein signals are received from a plurality of zones to control stages of temperature conditioning apparatus. The control circuit has a first time delay circuit for receiving a signal indicative of the need of the energization of temperature conditioning apparatus and a second time delay circuit connected to the output of the first time delay circuit for providing a signal to a control apparatus adapted to control the temperature conditioning apparatus. A first feedback circuit is connected to the input of the second time delay circuit for providing a feedback signal indicative of the operation of the control apparatus and a second feedback circuit provides a feedback signal to the second time delay circuit indicative of the operation of the temperature conditioning apparatus.

United States Patent 1 1 Kabat et al. A

ELECTRONIC CONTROL CIRCUIT WITH TIME DELAY OF MAIN AND FEEDBACK SllGNALSAssignee:

Filed:

Minn.

Oct. 2, 1972 Appl. No.: 294,418

Honeywell Inc., Minneapolis, Minn.

US. Cl .4 165/22, 236/1 C, 236/46,

Int. Cl. F24f 3/08, H03f 1/34 Field of Search 165/26, 22;

236/46 B, 78, l C; 330/103 References Cited UNITED STATES PATENTSRichardson 330/103 Nelson .r 165/22 X Jan. 15, 1974 PrimaryExaminer-William E. Wayner Attorney-Lamont B. Koontz et al.

[5 7] ABSTRACT An electronic control circuit particularly adaptable foruse in a heating and/or cooling control system wherein signals arereceived from a plurality of zones to control stages of temperatureconditioning apparatus. The control circuit has a first time delaycircuit for receiving a signal indicative of the need of theenergization of temperature conditioning apparatus and a second timedelay circuit connected to the output of the first time delay circuitfor providing a signal to a control apparatus adapted to control thetemperature conditioning apparatus. A first feedback circuit isconnected to the input of the second time delay circuit for providing afeedback signal indicative of the operation of the control apparatus anda second feedback circuit provides a feedback signal to the second timedelay circuit indicative of the operation of the temperatureconditioning apparatus.

7 Claims, 4 Drawing Figures COOL 22C 2 5- 1: -xt I1 I BRIDGE c iiiiz uli l6 CIRCUIT I l 2 aoH T l l l T 22H HTG CON 24 J r' l l l o msa O "V T23-C I I3 I ZONES l\. a 1 x \J \J a llkJ T lNG CONTROLLER SHEET 2 0? 3 mat ELECTRONIC CONTROL CIRCUIT WITH TIME DELAY OF MAIN AND FEEDBACKSIGNALS BACKGROUND AND SUMMARY OF THE INVENTION In zone control systemssuch as the system disclosed in the United States patents toElmer A.Carlson US Pat. No. 3,206,120 issued Sept. 14; 1965, to Bernard K. BetzU.S. Pat. No. 3,482,623 issued Dec. 9, 1969, to Lorne W. Nelson US. Pat.No. 3,567,115 issued Dec. 7, 1970, and Joseph E. Hogel US. Pat No.3,568,760 issued Mar. 9, 1971, the need for stability in the controlcircuitry has been recognized. In many prior art electronic controlsystems the use of feedback circuits for stability have been used;however, with such feedback signals the speed at which these feebacksignals take effect also is a factor in the stability of the controlcircuit. In the mentioned Carlson patent a time delay in the feedbacksignal is accomplished by the time required for a heater to affect thethermostat. In other prior art electronic control circuits a time delayis interposed in the individual feedback circuits to provide stability.

The present invention is concerned with an electronic control circuitproviding two types of feedback signals and time delay for both a maininput signal to the control circuit as well as the feedback signals witha minimum amount of electronic components to reduce the cost of thecontrol circuit and still maintain a high degree of stability.Specifically, the main input signal to the control circuit passesthrough a first time delay circuit and then on to a second time delaycircuit to provide the total amount of time delay necessary for the maininput signal. The two feedback signals, a first indicative of theoperation of the main control circuit and a second indicative of theoperation of the temperature conditioning apparatus are fed into thesecond time delay circuit to modify the effect of the main input signal.

FIG. 1 is a schematic showing of a niulti-zone temperature controlsystem making use of the electronic control circuit,

FIG. 2 is a block diagram of the main control circuit,

FIG. 3 is a circuit diagram of the zone bridge control circuit forproviding the main control circuit input signal and the control of thezone damper, and

FIG. 4 is a circuit diagram of the main control circuit shown in FIG. 2.

DESCRIPTION OF THE INVENTION Referring to FIG. I a zone control systemis shown for controlling the temperature in zones or spaces and 111 byapparatus such as that shown in the Lorne W. Nelson patent. Conditionedair is supplied from a hot deck or duct 12 and a cold deck or duct I3 toeach of the zones by an amount depending upon the position of the zonedampers controlled by the zone damper motors l4 and 14' through linkagesor output connections 16 and 16. Thermostats l5 and I5 respond to thetemperatures of the zones and by means of zone bridge control circuits20 and 20, the positions of the zone damper motors are selected tosupply the correct amount of air to the zones from either the hot orcold deck.

Associated with temperature conditioning apparatus or heat or coolingapparatus is a main control network circuit or central processor 22.Heat source or heat exchanger 21 is controlled by a main heating controlnetwork circuit 221-1 and a cooling source or heat exchanger 23 iscontrolled by a main cooling control network circuit 22C. An output fromeach of control circuits 20 and 20' is connected to a main input ofcontrol circuits 22H and 22C. In addition to the control of damper motor14 by zone thermostat 15, the control of the outputs of the temperatureconditioning sources 21 and 23 are controlled in a manner as broadlydisclosed in the Joseph E. Hogel patent. The zone thermostat firstcontrols the damper to increase the flow of air to the zone until thedamper is wide open and then the zone thermostat readjusts the decktemperature by increasing the output of either the heating or coolingconditioning apparatus 21 and/or 23. Associated with each of the maincontrol circuits 22H and 22C is a deck sensor or temperature responsiveelement 24 and 25 for providing a signal indicative of the temperatureof the air in the hot and cold decks 12 and 13. The number of zones isnot limited to the number shown, as two zones were selected forexplanation purposes only.

Referring to FIG. 2 a block schematic diagram of the cooling portion 22Cof the control circuit 22 is shown. A main input signal is received atinput 30C which is indicative of the temperature conditioning load ofthe zone having the greatest load. The input signal is fed into anamplifier and first time delay network circuit 31 which has an output at32 connected to an amplifier and time delay network circuit 33 for notonly receiving the main input signal through circuit connection 32 butfor summing signals on circuit connection 72. The output at 40 ofnetwork circuit 33 is connected to a temperature conditioning controlapparatus, main con trol circuit or controller 41 for controlling theoutput of the temperature conditioning apparatus or heat exchanger 23 inthe cold deck 13.

A feedback circuit 42 is connected to apparatus 41 for providing anegative feedback signal to the input 34 indicative of the operation oftemperature conditioning control apparatus 41 to reduce the effect ofsaid main input signal by counteracting the main signal. A secondfeedback circuit 43 is connected to deck temperature responsive element25 to provide a negative feedback signal to input 35 indicative of thetemperature of the air in deck 13 which is the function of the operationof the temperature conditioning apparatus 23 to reduce the'effect ofsaid main input signal. Specifically reviewing the control circuit ofFIG. 2. Upon a change in level of the main signal received at input 30C,the change is delayed through first time delay circuit 31 and secondtime delay circuit 33 for its effect upon a change in the operation ofcontrol apparatus 41 which changes the output of the temperatureconditioning apparatus 21. The change in the operation of controlapparatus 41 produces a signal which is fed-back through circuit 42 andsummed with the main signal but delayed by the second time delay circuit33. Similarly, any change in the output of the temperature responsiveelement 25 brings about a change in the operation of apparatus 41 aftera time delay caused by circuit 33. With the control circuit 22C, a firsttotal time delay for the main signal is accomplished by the first andsecond time delay circuits 31 and 33. The effect of the change in thesignal of the temperature responsive element 25 connected to the input35 through the feedback circuit 43 and the operation of apparatus 41connected through feedback circuit 42 are summed with the main signalcircuit and delayed by time delay circuit 33. With the common use of thesecond time delay circuit 33 for both the main signal and the feedbacksignals a smaller number of components resulting in a more economicalcontrol circuit results as will be seen in a more specific descriptionof the circuit shown in FIG. 4.

Referring to FIG. 3 the control circuit 20 which is used for each zoneis shown in detail. A temperature responsive resistance element orthermostat is connected in a rebalanced bridge circuit 50 of the typedisclosed in the US. application of B. Hubert Pinckaers, Ser. No 273,245filed July 19, 1972. Circuit 50 is connected to the input of anamplifier unit 51 providing an output signal through circuits 52 and 53to control the energization of damper motor 14. The damper motor outputconnection 16 is also connected to the rebalance potentiometer in thebridge circuit 50 to rebalance the bridge upon any change in theresistance of thermostat 15 to provide a position control of dampermotor 14 for every temperature of the thermostat in a first range oftemperatures.

Upon the temperature of thermostat 15 exceeding the first range, therebalance potentiometer of the bridge circuit can no longer rebalancebridge 50 and a bridge output after being amplified by amplifier 51provides a heating signal or cooling signal over circuits 30H and 30Chaving a magnitude depending upon the temperature at the thermostat inthe second range of temperatures. As mentioned each zone contains a zonecircuit 21. Contained in the circuits 30H and 30C are diodes 54 and 55which when back biased prevents the signal of amplifier 51 from passingthrough the diodes. Circuit of the zone having the largest load demandor heat signal or cool signal over circuits 301-1 and C selectivelypasses a signal through the diodes to the input of the control circuit22 to either control the heating or cooling apparatus.

Referring to FIG. 4 the specific circuit of the control circuit 22 isshown which when described in the block diagram of FIG. 2 had a coolingportion 22C and a heating portion 22H. Since the two portions areidentical for all practical purposes only the cooling portion 22C willbe described in any detail. The main cooling signal of circuit 30C isconnected into a first amplifier unit 60 which has its output connectedto the input of the amplifier and time delay circuit 31. Specificallythe time delay is accomplished by a resistance 61 and a capacitor 62connected in parallel between the output and input of the amplifier unit63. Amplifier unit 63, as well as other amplifiers to be mentioned, isan integrated circuit chip of a conventional type available fromelectrical suppliers such as an MC3301P unit available from MotorolaSemiconductor Products Inc. The output of circuit 31 is connected byconnection 32 to an amplifier, time delay and summing circuit 33 whichis made up of an ampiifier 64 and amplifier 65. A resistance 70 and acapacitor 71 are connected between the output and input of amplifier 65to provide the time delay. Also connected to circuit 33 is the feedbacksignals over a circuit 72 which has the feedback output on circuit fromcircuit 43 of the cold deck temperature responsive element 25 and thefeedback output circuit 34 made up of signals over 34A and 34B which arebrought about by the operation of the two stages (cool 1 and 2) ofcontroller 41.

The output of the second time delay circuit 33 is connected to the input40 of control circuit 41 which brings about the energization of a firstrelay and a second relay 81 in a sequential staging manner to operatetwo stages of conventional cooling apparatus associated with the coolingchanging apparatus 23 depending upon the level of the main input signalreceived from the thermostat of the zone having the greatest coolingload.

OPERATION OF THE INVENTION Upon a call for cooling thermostat 15 of zone10 as shown in FIG. 1, a first range of increase in the zone temperaturecauses the zone damper motor to open the damper to allow more air toflow from cold deck 13 and less air to flow from hot deck 12. If thezone temperature continues to increase above the first range oftemperature, the thermostat causes a main cooling signal to be developedin circuit 20 as shown in FIG. 3 to provide the main cooling outputsignal over circuit 30C to cooling control circuit 22C which is shown inblock diagram in FIG. 2. As the main cooling control signal over circuit30C increases, an increase in the output of the temperature conditioningapparatus 23 results by the sequential operation of the stages (cool 1and 2) of cooling apparatus to cool the air passing through duct 13.

In order to maintain stability in such a control system, any change inthe main control signal over input 30C is delayed to prevent a suddenreaction by the control apparatus 41. Specifically the change of theinput signal can take place if a change in the setpoint of thethermostat 15 was brought about by a manual adjustment of the thermostatover a wide range in temperature or electrical noise pick up in theelectrical circuit. The time delay interposed in the effect of the mainsignal over circuit 30C on the apparatus 41 is brought about by thetotal time delay produced by circuits 31 and 33.

The feedback from the condition control apparatus 41 and the temperatureresponsive element 25 are summed and connected into the second timedelay circuit 33 to make use of the same time delay network which isused with the main signal. Both of the feedback signals and the mainsignal over circuit 32 are summed by means of a single amplifier network33 which also provides additional time delay for the main signal andtime delay to slow the effects of the feedback signals and add stabilityto the control circuit. With the use of the single circuit 33 to providethe amplification time delay and summing, the control circuit operationis accomplished with a fewer number of components to reduce the cost ofthe apparatus.

Specifically, with a steady load condition in zone 10 causing at input30C from zone thermostat 15, the combined feedbacks of circuits 42 and43 result in a predetermined cycling rate of controller 41. Thesefeedbacks result from the operation of at least one stage of controller41 and some predetermined reduction of the deck air temperature at 25due to the effect of heat exchanger 23. Assuming that a change in theload condition of zone 11 takes place to reduce air flow in deck 13, asudden drop in the deck air temperature at element 25 takes place. Thedrop in temperature increases the feedback signal of circuit 43 toreduce the effect of the main signal on controller 41 to increase thecycling rate of controller 41. With an increase in the cycling rate, thefeedback signal of circuit 42, in combination with time delay 33,decreases resulting in a lessing of the increase in cycling rate ofcontroller 41 which is desirable to lengthen equipment life. Thespecific operation is similar for the heating circuit 22H and is theneven more important as deck temperature in the heating apparatus tendsto change more rapidly upon a reduction of airflow in the deck 12especially when electric heating is used at heat source 21.

The embodiments of the invention in which an exclusive property or rightis claimed are defined as follows:

1. In a zone control system having a zone damper motor for each zone forcontrolling the supply of hot and cold air to the zone in response to azone thermostat connected thereto by a control circuit having heatingand cooling control output circuits with signals indicative of thetemperature of the air needed for that zone for heating and cooling andhaving a central processor to which the output circuits are connected sothe zone of the highest demand controls heating and cooling apparatusfurnishing the supply of hot and cold air, the improvement comprising:

a control circuit in the central processor comprising an input circuitselectively connected to one of said output circuits for receiving asignal indicative of the temperature conditioning load of the zonehaving the greatest temperature conditioning load,

a first time delay circuit connected to said input circuit to receiveaaid input signal for delaying any changes in said input signal by afirst predetermined amount,

a second time delay circuit connected to receive an output of said firsttime delay circuit,

control means adapted to control temperature conditioning apparatus inresponse to an output of said second time delay circuit,

a first feedback signal circuit from said control means for providing afeedback signal indicative of the operation of said control means,

asecond feedback signal circuit adapted to respond to a conditionindicative of the operation of the temperature conditioning apparatusfor providing a feedback signal, and

circuit means connecting said first and second feedback signal to saidsecond time delay circuit.

2. In a control circuit adapted for receiving a main signal indicativeof the need of operation of temperature conditioning apparatusand-adapted to control the temperature conditioningapparatus,comprising:

first circuit means adapted to receive the main signal, said circuitmeans providing a predetermined time delay between the effect of changesof the signal and changes in a first output signal of said circuitmeans,

second circuit means connected to receive said first output signal, saidsecond circuit means providing a predetermined time delay between theeffects of changes of said first output signal and changes in a secondoutput signal of said second circuit means,

control circuit means adapted to control temperature conditioningapparatus, said control circuit being connected to respond to saidsecond output signal,

first feedback circuit means providing a first feedback signal to saidsecond circuit means indicative of the operation of said control circuitmeans, and

second feedback circuit means adapted to provide a second feedbacksignal to said second circuit means indicative of the effect of theoperation of the temperature conditioning apparatus.

3. The invention of claim 1 wherein said second time delay circuitcomprises a summing circuit means for receiving said input signal fromsaid first time delay circuit, and said feedback signals from said firstand second feedback circuits.

4. The invention of claim 1 wherein said control means comprises astaging control device for controlling at least two stages oftemperature conditioning apparatus in sequence,

said first feedback signal circuit means providing a feedback signalupon the operation of each of said two stages.

5. The invention of claim 2 wherein,

said first feedback signal is a negative signal for counteracting saidmain signal to reduce its effect temporarily on said control circuitmeans, and

said second feedback signal is a negative signal for counteracting saidmain signal to reduce its effect temporarily on said control circuitmeans.

6. The invention of claim 5 wherein,

said control circuit is a stage control apparatus adapted forcontrolling at least two stages of temperature conditioning apparatus insequence,

said first feedback signal is made up of several separate signals eachbrought about by the operation of one of said stages of said stagecontrol apparatus.

7. The invention of claim 6 wherein said second feedback signal circuitmeans comprises,

1. In a zone control system having a zone damper motor for each zone forcontrolling the supply of hot and cold air to the zOne in response to azone thermostat connected thereto by a control circuit having heatingand cooling control output circuits with signals indicative of thetemperature of the air needed for that zone for heating and cooling andhaving a central processor to which the output circuits are connected sothe zone of the highest demand controls heating and cooling apparatusfurnishing the supply of hot and cold air, the improvement comprising: acontrol circuit in the central processor comprising an input circuitselectively connected to one of said output circuits for receiving asignal indicative of the temperature conditioning load of the zonehaving the greatest temperature conditioning load, a first time delaycircuit connected to said input circuit to receive said input signal fordelaying any changes in said input signal by a first predeterminedamount, a second time delay circuit connected to receive an output ofsaid first time delay circuit, control means adapted to controltemperature conditioning apparatus in response to an output of saidsecond time delay circuit, a first feedback signal circuit from saidcontrol means for providing a feedback signal indicative of theoperation of said control means, a second feedback signal circuitadapted to respond to a condition indicative of the operation of thetemperature conditioning apparatus for providing a feedback signal, andcircuit means connecting said first and second feedback signal to saidsecond time delay circuit.
 2. In a control circuit adapted for receivinga main signal indicative of the need of operation of temperatureconditioning apparatus and adapted to control the temperatureconditioning apparatus, comprising: first circuit means adapted toreceive the main signal, said circuit means providing a predeterminedtime delay between the effect of changes of the signal and changes in afirst output signal of said circuit means, second circuit meansconnected to receive said first output signal, said second circuit meansproviding a predetermined time delay between the effects of changes ofsaid first output signal and changes in a second output signal of saidsecond circuit means, control circuit means adapted to controltemperature conditioning apparatus, said control circuit being connectedto respond to said second output signal, first feedback circuit meansproviding a first feedback signal to said second circuit meansindicative of the operation of said control circuit means, and secondfeedback circuit means adapted to provide a second feedback signal tosaid second circuit means indicative of the effect of the operation ofthe temperature conditioning apparatus.
 3. The invention of claim 1wherein said second time delay circuit comprises a summing circuit meansfor receiving said input signal from said first time delay circuit, andsaid feedback signals from said first and second feedback circuits. 4.The invention of claim 1 wherein said control means comprises a stagingcontrol device for controlling at least two stages of temperatureconditioning apparatus in sequence, said first feedback signal circuitmeans providing a feedback signal upon the operation of each of said twostages.
 5. The invention of claim 2 wherein, said first feedback signalis a negative signal for counteracting said main signal to reduce itseffect temporarily on said control circuit means, and said secondfeedback signal is a negative signal for counteracting said main signalto reduce its effect temporarily on said control circuit means.
 6. Theinvention of claim 5 wherein, said control circuit is a stage controlapparatus adapted for controlling at least two stages of temperatureconditioning apparatus in sequence, said first feedback signal is madeup of several separate signals each brought about by the operation ofone of said stages of said stage control apparatus.
 7. The invention ofclaim 6 wherein said sEcond feedback signal circuit means comprises,circuit means adapted to respond to an output signal of a temperatureresponsive device responding to the temperature of air in a duct as thetemperature changes upon the operation the temperature conditioningapparatus.